(function(win) {
        var doc = win.document;
        var docEl = doc.documentElement;
        var tid;

        function refreshRem() {
            var width = docEl.getBoundingClientRect().width;
            if (width > 640) {
                width = 640;
            }
            var rem = width / 6.4;
            docEl.style.fontSize = rem + 'px';
        }
        win.addEventListener('resize', function() {
            clearTimeout(tid);
            tid = setTimeout(refreshRem, 300);
        }, false);
        win.addEventListener('pageshow', function(e) {
            if (e.persisted) {
                clearTimeout(tid);
                tid = setTimeout(refreshRem, 300);
            }
        }, false);
        refreshRem();
    }

)(window);